Resistive reach
The resistive reach in reverse direction must be set longer than the longest reverse zones.
In blocking schemes it must be set longer than the overreaching zone at remote end that
is used in the communication scheme. In equation
63 the index ZmRv references the
specific zone to be coordinated to.
ZmRv
RFltREvPG 1.2 RFPG³ ×
EQUATION1726 V1 EN (Equation 63)
Phase-to-phase fault in forward direction
Reactive reach
The reach in reactive direction is determined by phase-to-ground reach setting X1. No
extra setting is required.
Resistive reach
In the same way as for phase-to-ground fault, the reach is automatically calculated based
on setting X1. The reach will be X1/tan(60°) =X1/√(3).
Fault resistance reach
The fault resistance reaches in forward direction RFItFwdPP, must cover RFPP
Zm
with at
least 25% margin. RFPP
Zm
is the setting of fault resistance for phase-to-phase fault for the
longest overreaching zone to be covered by FDPSPDIS (21), see figure 68. The minimum
recommended reach can be calculated according to equation 64.
EQUATION1318-ANSI V1 EN (Equation 64)
where:
RFPP
Zm
is the setting of the longest reach of the overreaching zones that must be covered by FDPSPDIS
(21).
Equation 64 modified is applicable also for the RFltRevPP as follows:
min
Re 1.25
zmRv
RFlt vPP RFPP³ ×
EQUATION2264-ANSI V1 EN
Equation 64 is also valid for three-phase fault. The proposed margin of 25% will cater for
the risk of cut off of the zone measuring characteristic that might occur at three-phase fault
when FDPSPDIS (21) characteristic angle is changed from 60 degrees to 90 degrees
(rotated 30° anti-clock wise).
1MRK 506 334-UUS A Section 6
Impedance protection
143
Application manual
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